This invention relates to a polypropylene monofilament suture exhibiting improved properties, e.g., reduced strain energy and improved knot security, and to a process for its manufacture.
Sutures fabricated from polypropylene homopolymers and copolymers and from polymer blends containing polypropylene are disclosed in, among others, U.S. Pat. Nos. 3,359,983, 3,630,205, 4,520,822, 4,557,264, 4,620,542, 4,621,638 and 4,911,165 and in U.K. Patent Specification No. 1,588,031 and European Patent Application No. 415,783.
Thus, e.g., in accordance with U.S. Pat. No. 3,630,205, following extrusion an isotactic polypropylene monofilament is quenched to effect its solidification and drawn, or stretched, from six to seven times its original length at elevated temperature resulting in its orientation and an increase in its tensile strength. The stretched monofilament is then collected on a spool for subsequent processing, specifically, an annealing operation which results in the shrinkage of the suture. The various conditions of the extrusion, stretching and annealing steps are indicated to be important for obtaining the desired polypropylene monofilament suture, one which is characterized by an ultimate elongation of from 35 to 63 percent.
The polypropylene monofilament suture manufacturing process of U.S. Pat. No. 4,911,165 is said to provide a suture exhibiting improved compliance while retaining the excellent properties of prior polypropylene monofilament sutures. An increase in the draw ratio during orientation and the allowed shrinkage during annealing is credited with resulting in a monofilament suture of lower modulus at a given level of tensile strength.